Physical quantity measuring devices each including a sensor unit for detecting a physical amount (e.g. pressure of a target fluid) and a circuit portion for processing signals outputted by the sensor unit have been known. Some of the physical quantity measuring devices are designed not to transmit heat of a target fluid to the circuit portion.
Typical examples of this type of physical quantity measuring device include a pressure sensor including: a pressure receiver provided with a sensor chip for detecting pressure; and a pressure transmitter provided with cooling fins for dissipating heat generated at the pressure receiver (Patent Literature 1; JP 2003-42869 A).
Another one of the typical examples of the physical quantity measuring device is an electrostatic capacitance pressure sensor including: a sensor housing that houses an electrostatic capacitance sensor for detecting gas pressure and a heater for heating the sensor; a circuit housing that houses a circuit portion for processing signals outputted by the sensor; and a heat-transmission blocker that defines a partition between the sensor housing and the circuit housing (Patent Literature 2; JP 4563312 B2).
The typical example according to Patent Literature 1, which includes the cooling fins on the pressure transmitter, requires convection around the cooling fins in order to efficiently dissipate the heat. If the cooling effect provided by cooling fins is insufficient, the heat at the pressure receiver is transmitted to the circuit portion through the pressure transmitter to deteriorate the measurement accuracy.
According to the typical example disclosed in Patent Literature 2, when the surroundings of the circuit housing are cooled, dew condensation is likely to be caused inside the circuit housing. If the pressure sensor is disposed so that the circuit housing is located at a lower side and the sensor housing is located at an upper side, the dew condensation caused at the circuit housing may flow to reach the circuit portion, thereby causing malfunction and the like.